The high diversity and endemicity of mammals is related to the many niches found in the tropical rain forest of Borneo and past Pleistocene events within the Sundaland region.
The mammal species of Borneo include 288 species of terrestrial and 91 species of marine mammals recorded within the territorial boundaries of Brunei, Indonesia and Malaysia. The terrestrial mammals are dominated by the Chiroptera (102 species of bats) and rodents (61 species of rats and mice).
Borneo is abundant in bird species and is is a favourite destination for tropical bird watchers. There are about 600 species of birds and 37 are endemic to Borneo.